Arc-resistant switchgear enclosures house medium voltage electrical switchgear components such as potential transformers (PT), fuses, circuit breakers, etc. A typical enclosure has plural compartments, with each compartment housing one or more electrical components. Medium voltage generally is in the 5-38 KVA range.
During normal operation, the switchgear components generate heat and require air circulation for cooling. The enclosure has vents to provide cooling. For example, an intake or inlet vent may be on or near a front access door. Air is drawn in through the inlet vent, is heated by the switchgear components, rises and exits through a vent in the top of the enclosure, into a plenum.
However, such medium voltage electrical components can experience arc faults. An arc fault creates an explosion of hot gasses which can endanger nearby personnel and equipment.
In order to protect nearby personnel and equipment, enclosures are metal clad and are designed to contain the explosion and vent the explosive gasses in a controlled manner. Personnel and equipment at the front, sides and rear of an enclosure are protected by the walls of the enclosure. The explosive gasses are typically vented up into the plenum which channels the explosive gasses to a safe area, such as a building exterior.
When an arc fault explosion occurs, the intake vent or vents are closed by the force of the explosion. In contrast, the outlet vent is kept open to vent the explosive gasses into the plenum. However, outlet vents for the remaining compartments are closed. This is particularly true for type 2C enclosures, where an arc-fault explosion in one compartment does not enter the remaining compartments, thus preserving the switchgear in those other compartments.
The challenge lies in designing an outlet vent that is normally open to allow for ventilation and cooling of the switchgear components, but suddenly closes during an arc-fault explosion in another compartment and remains closed thereafter.